Faculty of Health, School of Exercise and Nutrition Sciences, Queensland University of Technology (QUT), Brisbane, QLD, Australia.
Department of Physical Education, Federal University of Mato Grosso, Cuiaba, MT, Brazil.
Eur J Appl Physiol. 2023 Mar;123(3):633-643. doi: 10.1007/s00421-022-05089-w. Epub 2022 Nov 23.
Deficits in muscle performance could be a consequence of a reduced ability of a motor neuron to increase the rate in which it discharges. This study aimed to investigate motor unit (MU) discharge properties of each triceps surae muscle (TS) and TS torque steadiness during submaximal intensities in runners with Achilles tendinopathy (AT).
We recruited runners with (n = 12) and without (n = 13) mid-portion AT. MU discharge rate was analysed for each of the TS muscles, using high-density surface electromyography during 10 and 20% isometric plantar flexor contractions.
MU mean discharge rate was lower in the gastrocnemius lateralis (GL) in AT compared to controls. In AT, GL MU mean discharge rate did not increase as torque increased from 10% peak torque, 8.24 pps (95% CI 7.08 to 9.41) to 20%, 8.52 pps (7.41 to 9.63, p = 0.540); however, in controls, MU discharge rate increased as torque increased from 10%, 8.39 pps (7.25-9.53) to 20%, 10.07 pps (8.89-11.25, p < 0.001). There were no between-group difference in gastrocnemius medialis (GM) or soleus (SOL) MU discharge rates. We found no between-group differences in coefficient of variation of MU discharge rate in any of the TS muscles nor in TS torque steadiness.
Our data demonstrate that runners with AT may have a lower neural drive to GL, failing to increase MU discharge rate to adjust for the increase in torque demand. Further research is needed to understand how interventions focussing on increasing neural drive to GL would affect muscle function in runners with AT.
运动神经元增加放电频率的能力下降可能导致肌肉性能受损。本研究旨在探讨跟腱病（AT）跑者在亚最大强度下，每条比目鱼肌（TS）的运动单位（MU）放电特性以及 TS 扭矩稳定性。
我们招募了患有（n=12）和不患有（n=13）中段 AT 的跑者。在进行 10%和 20%等长跖屈收缩时，使用高密度表面肌电图分析 TS 肌肉的 MU 放电率。
与对照组相比，AT 患者的外侧腓肠肌（GL）MU 平均放电率较低。在 AT 患者中，GL MU 平均放电率并未随着从 10%峰值扭矩时的 8.24pps（95%CI 7.08 至 9.41）增加到 20%时的 8.52pps（7.41 至 9.63，p=0.540）而增加；然而，在对照组中，MU 放电率随着从 10%时的 8.39pps（7.25 至 9.53）增加到 20%时的 10.07pps（8.89 至 11.25，p<0.001）而增加。GM 和 SOL 的 MU 放电率在两组间没有差异。我们没有发现任何 TS 肌肉 MU 放电率变异系数或 TS 扭矩稳定性存在组间差异。
我们的数据表明，AT 跑者的 GL 神经驱动可能较低，无法增加 MU 放电率以适应扭矩需求的增加。需要进一步研究以了解针对增加 GL 神经驱动的干预措施如何影响 AT 跑者的肌肉功能。
